1. Technical Field of the Invention
The present invention relates to an apparatus for detecting malfunctions of electromagnetic brakes for braking motors incorporated in a robot and how to check malfunctions of the electromagnetic brakes.
2. Related Art
In robots such as industrial robots working in factories, brake mechanisms that brake electric motors to drive robot arms are essential in properly controlling the coordinates positions and attitudes of robot joints of the arms. In general, each of the brake mechanisms is provided with an electromagnetic brake braking a motor with an excitation coil and relays switching over between the current supply state (energized) and the current no-supply state (non-energized) of the brake.
This break mechanism may operate erroneously when the relay(s) causes a malfunction, even if the electromagnetic brake itself can work normally. For example, if the relay(s) works erroneously so as to unlock (i.e., release) the brake, the arm may drop down from the robot.
In order to avid such a drawback, there can be provided a countermeasure to adopt a regenerating brake making use of regenerating energy from a motor in cases where the relay malfunctions. However, this countermeasure is not sufficient, because the regenerating brake by itself cannot prevent the arm form dropping down, although it can make the dropping speed of the arm slower. To improve this insufficient situation, there may be applied a technique disclosed by Japanese Patent No. 3158914, where a brake mechanism is subjected to detection of a malfunction which may occur in relays for electromagnet brakes.
Practically, the malfunction detecting technique provided by the above reference publication is mainly directed to the detection of errors of relays used with wheels that move along the ground surface. When it is detected that a relay is malfunctioning, the brake is locked. This malfunction detecting technique can be applied to a brake for the wheels of electric-motor coach, in which the coach can be prevented from running out of control even if the relay is brought into its malfunctioning state.
However, when this kind of malfunction detecting technique is applied to an industrial robot, there remains a drawback which cannot be removed by this technique. That is, the arms of an industrial robot should move in the space, which means that the arms should resist the gravitational force. Hence, if the brake mechanism for motors driving arms causes a malfunction, the locking action is performed after detecting the malfunction, which results in an after-the-fact control. Accordingly, an arm may have dropped down already when the brake mechanism is activated. It is thus impossible to avoid the arms from drooping in a reliable manner.